This invention relates to compositions of fluorinated hydrocarbons and, more specifically, to azeotropic mixtures of perfluoropropane or 1,1,1,2,3,3,3-heptafluoropropane with dimethyl ether.
Closed-cell polyurethane foams are widely used for insulation purposes in building construction and in the manufacture of energy efficient electrical appliances. In the construction industry, polyurethane (polyisocyanurate) board stock is used in roofing and siding for its insulation and load-carrying capabilities. Poured and sprayed polyurethane foams are also used in construction. Sprayed polyurethane foams are widely used for insulating large structures such as storage tanks, etc. Pour-in-place polyurethane foams are used, for example, in appliances such as refrigerators and freezers plus they are used in making refrigerated trucks and railcars.
All of these various types of polyurethane foams require blowing agents for their manufacture. Insulating foams depend on the use of halocarbon blowing agents, not only to foam the polymer but primarily for their low vapor thermal conductivity, a very important characteristic for insulation value. Historically, polyurethane foams are made with CFC-11 as the primary blowing agent. Phenolic polymers have been foamed for insulation and they have very attractive flammability characteristics. These polymers are generally made with CFC-11 and CFC-113 blowing agents. Thermoplastics, such as polystyrene, have been foamed for insulation and polyolefins, such as polyethylene and polypropylene, have been foamed and are widely used in packaging. These thermoplastic foams are generally made with CFC-12. Many products designed for household, personal or industrial use are available as aerosol products. All such products utilize the pressure of a propellant gas or a mixture of propellant gases (i.e., a propellant gas system) to expel the active ingredients from the container. For this purpose, aerosols employ liquified gases which vaporize and provide the pressure to propel the active ingredients when the valve on the aerosol container is pressed open.
Many refrigeration applications, e.g., refrigerators and auto air conditioners, presently use CFC-12 as the refrigerant. The subject azeotropes offer environmentally acceptable substitutes for CFC-12.
Recently the long-term environmental effects of chlorofluorocarbons have come under substantial scientific scrutiny, because it has been postulated that these materials decompose in the stratosphere, under the influence of ultraviolet radiation to release chlorine atoms. Chlorine atoms are theorized to undergo chemical reaction in the stratosphere which could deplete the stratospheric ozone layer, which shields the earth from harmful ultraviolet radiation. A substantial reduction of stratospheric ozone could have a serious deleterious impact on the quality of life on earth.
There is a continuing need in this art for new materials having new combinations of properties for use as refrigerants, aerosol propellants, heat transfer media, gaseous dielectrics, fire extinguishing agents, blowing agents for polyolefins, polystyrene and polyurethanes and as power cycle working fluids. Such compositions must be potentially environmentally safe and function effectively as substitutes for chlorofluorocarbons that are used for these applications, e.g., Refrigerant 502.
There is a limit to the number of single fluorinated hydrocarbon substances which can be candidates as environmentally safe materials. Mixtures of known materials, however, might be used if the desired combination of properties could be found in a given mixture. Simple mixtures, however, create problems in design and operation of refrigeration and other equipment because of component segregation in both the vapor and liquid phases. To avoid component segregation problems, it is particularly desirable to discover new substantially constant boiling fluorocarbon blends. Such blends would not suffer from component segregation problems. Unfortunately, it is not possible to predict the formation of constant boiling compositions, e.g., azeotropes, thus complicating the search for novel compositions which possess the desired combination of properties. There is a need for substantially constant boiling compositions that have properties which make them particularly useful as refrigerants, aerosol propellants, heat transfer media, gaseous dielectrics, fire extinguishing agents, blowing agents for foaming thermoplastics such as polyolefins, polystyrene, polyurethanes and phenolics, such as phenolformaldehydes, resins and that are potentially environmentally safe so that they can be used as substitutes for the chlorofluorocarbons that are now used for these applications.